1. Field of the Invention
The present invention relates to a driving circuit and, more particularly, to a programmable driving circuit for being applied in an organic light emitting diode (OLED) panel.
2. Description of Related Art
Conventionally, organic light emitting diode (OLED) panel is composed of a plurality of thin-film organic light emitting diodes. The driving mode of the OLED panel may be a constant current driving or a constant voltage driving mode. FIGS. 5 and 6 illustrate the system architectures of OLED panels driven by a constant voltage driving circuit and by a constant current driving circuit, respectively. Typically, the OLED panel is of a common cathode configuration. Therefore, the driving circuit is divided into a column driving circuit 51 or 61 and a row driving circuit 52, wherein the column driving circuit 51 or 61 is provided to output current to anodes of OLEDs 54 of a corresponding column in response to input column data from a column data shift register 53. Furthermore, the row driving circuit 52 is provided to sink the conducting current of a row of the common-cathode OLEDs 54 turned on by scanning line pulse of a row scanning shift register 55.
In design an OLED driving system, the column driving circuit 61 of the constant current driving circuit generally comprises a plurality of constant current column driver cells 71, as shown in FIG. 7, and a reference bias generator 62. The column driving circuit 51 of the constant voltage driving circuit is generally implemented by a plurality of constant voltage column driver cells 81, as shown in FIG. 8. The output current of each of the column driver cells 71 and 81 is controlled by input column driving signal of a column data shift register 53. In order to rapidly eliminate the residual image caused by the junction capacitance and the wiring stray capacitance of the OLEDs 54, a discharge device MND controlled by discharge signal DIS is provided in the column driver cells 71 and 81 of the column driving circuit 51 and 61, respectively. The discharge device MND is conducted for a short period of time at the beginning or end of each scanning line for leaking off the charge stored in the junction capacitors and the stray capacitors of OLEDs. Moreover, a pre-charge device NPPRE is usually provided in the constant current column driver cell 71. The pre-charge device MPPRE is controlled by a pre-charge control terminal PRE-CHARGE for pre-charging OLEDs to be turned on.
The row driving circuit 52 is composed of a plurality of row driver cells 521, each being an inverter or an amplifier capable of sinking a large current, so as to sink the conducting current from a whole row of OLEDs at a row input terminal ROWI and maintain a relatively low voltage drop (e.g., smaller than IV).
Because the requirements of the characteristics of the column driving circuit and row driving circuit are different, the system design of the OLED panel usually employs a column driving integrated circuit (IC) and a row driving IC that are separately designed and manufactured. However, to satisfy various requirements in different applications, there is required a variety of combinations of pixels for the OLED panel, such as 64 columnxc3x9716 row, 48 columnxc3x9732 row, 32 columnxc3x9748 row, 16 columnxc3x9764 row, or an even a larger one. Thus, a plurality of different column driving ICs and a plurality of different row driving ICs must be developed for fulfilling such needs, resulting in increasing the manufacturing cost and wasting the resource. Therefore, it is desirable for the above conventional OLED driving circuit to be improved.
An object of the present invention is to provide a programmable driving circuit which can be programmed to provide a desired number of column driver cells and row driver cells based on the combination of pixels of OLED panel, thus eliminating the need to design and manufacture various column driving ICs and row driving ICs as experienced by the prior art.
According to one aspect, the present invention which achieves the object relates to a programmable driving circuit having a plurality of driver cells, each comprising: a switch transistor having a source connected to a supplied voltage; a current output transistor having a source connected to a drain of the switch transistor, and a drain provided as a column/row output terminal of the driver cell; a discharge transistor having a drain connected to the drain of the current output transistor, and a source connected to ground; a first multiplexer having an output terminal connected to the gate of the switch transistor, a first input terminal and a second input terminal provided as a row input terminal and a column input terminal of the driver cell, respectively; a second multiplexer having an output terminal connected to the gate of the discharge transistor, a first input terminal connected to the row input terminal, and a second input terminal provided as a discharge control terminal; and a third multiplexer having an output terminal connected to the gate of the current output transistor, a first input terminal connected to ground, and a second input terminal connected to a bias output terminal, wherein each of the first, the second, and the third multiplexers has a control terminal connected together for being provided as a programmable control terminal.
According to another aspect, the present invention which achieves the object relates to a programmable driving circuit having a plurality of driver cells, each comprising: a switch transistor having a source connected to a supplied voltage; a current output transistor having a source connected to a drain of the switch transistor, and a drain provided as a column/row output terminal of the driver cell; a discharge transistor having a drain connected to the drain of the current output transistor, and a source connected to ground; a pre-charge transistor having a source and a drain connected to the source and the drain of the current output transistor, respectively; a first multiplexer having an output terminal connected to a gate of the switch transistor, a first input terminal and a second input terminal provided as a row input terminal and a column input terminal of the driver cell, respectively; a second multiplexer having an output terminal connected to a gate of the discharge transistor, a first input terminal connected to the row input terminal, and a second input terminal provided as a discharge control terminal; a third multiplexer having an output terminal connected to a gate of the current output transistor, a first input terminal connected to ground, and a second input terminal connected to a bias output terminal; and a fourth multiplexer having an output terminal connected to a gate of the pre-charge transistor, a first input terminal connected to the supplied voltage, and a second input terminal provided as a discharge control terminal, wherein each of the first, the second, the third, and the fourth multiplexers has a control terminal connected together for being provided as a programmable control terminal.
According to yet another aspect, the present invention which achieves the object relates to a programmable driving circuit having a plurality of driver cells, each comprising: a switch transistor having a source connected to a supplied voltage; a current output transistor having a source connected to a drain of the switch transistor, and a drain provided as a column/row output terminal of the driver cell; a discharge transistor having a drain connected to the drain of the current output transistor and a source connected to ground; an auto-clamped pre-charge transistor having a source and a drain connected to the source and the drain of the current output transistor, respectively; a first multiplexer having an output terminal connected to a gate of the switch transistor, a first input terminal and a second input terminal provided as a row input terminal and a column input terminal of the driver cell, respectively; a second multiplexer having an output terminal connected to a gate of the discharge transistor, a first input terminal connected to the row input terminal, and a second input terminal provided as a discharge control terminal; and a third multiplexer having an output terminal connected to gates of the current output transistor and the auto-clamped pre-charge transistor, a first input terminal connected to ground, and a second input terminal connected to a bias output terminal, wherein each of the first, the second, and the third multiplexers has a control terminal connected together for being provided as a programmable control terminal.
Other objects, advantages, and novel features of the invention will become more apparent from the detailed description when taken in conjunction with the accompanying drawings.